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Astron. Astrophys. 358, 104-112 (2000)

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2. The samples

2.1. FR I radio galaxies

Our complete sample of radio galaxies comprises all the FR I sources belonging to the 3CR catalogue (Spinrad et al. 1985), morphologically identified as FR I. The redshifts of these objects span the range [FORMULA] - 0.29, with a median value of [FORMULA], and the total radio luminosities at 1.4 GHz are between [FORMULA] and [FORMULA] erg s-1 Hz-1 ([FORMULA] km s-1 Mpc-1 and [FORMULA] are adopted hereafter). We exclude from the original sample the peculiar object 3C 386, as discussed in Paper I. The optical and radio data are from Paper I, while the X-ray ones from Hardcastle & Worral (1999). The optical data are extrapolated to the V band using a spectral index [FORMULA] ([FORMULA]).

2.2. Radio and X-ray selected BL Lacs samples

We consider both the complete sample of 34 radio selected BL Lacs derived from the 1Jy catalog (Stickel et al. 1991, Kühr et al. 1981), and the BL Lac sample selected from the Einstein Slew survey (Elvis et al. 1992, Perlman et al. 1996), which comprises 48 objects, and it is nearly complete. The extended radio power (at 1.4 GHz) [FORMULA] [erg s-1 Hz-1] spans the ranges [FORMULA] (1Jy BL Lacs, Kollgaard et al. 1996) and [FORMULA] (Slew survey BL Lacs, Kollgaard et al. 1996, Perlman et al. 1996); the redshifts are between 0.049 and 1.048 (median [FORMULA]) and between 0.031 and 0.513 (median [FORMULA]) for the two samples, respectively (the redshifts of the Slew BL Lacs are taken from the data collected by Fossati et al. 1998).

Instead of classifying BL Lacs according to their selection spectral band, in the following we adopt the definitions of high and low energy peaked BL Lacs (HBL and LBL respectively), which are based on the position of the (synchrotron) emission peak in the spectrum and therefore more indicative of the physical characteristics of the objects (Giommi & Padovani 1994, Fossati et al. 1998). Of the 34 objects belonging to the 1 Jy sample, 32 are classified as LBL and 2 as HBL, while of the 48 X-ray selected BL Lacs, 40 are HBL and 8 are LBL.

The spectral data for both samples of BL Lacs are taken from Fossati et al. 1998.

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© European Southern Observatory (ESO) 2000

Online publication: June 26, 2000